Electrical steering device for motor vehicles

ABSTRACT

The invention relates to an electrical steering device for a motor vehicle, comprising an electromotor with a worm gear. Said worm gear consists of a worm and a worm wheel ( 14 ) which is coupled to an input shaft and which has a gear rim ( 23 ). The worm wheel ( 14 ) forms one of the two coupling parts of an elastic compensation coupling ( 14, 16 ) that are to be intercoupled, the other coupling part ( 16 ) being connected to the input shaft in a rotationally fixed manner. The two coupling parts ( 14, 16 ) are intercoupled by one or more elastic spacers ( 17 ) only.

FIELD OF THE INVENTION

[0001] The present invention relates to an electrical steering system.

BACKGROUND INFORMATION

[0002] Electrical steering systems may have an input shaft, that ismechanically linked to a steering handwheel, which is used to transmit atorque required for steering wheels to be steered. An output member ismechanically connected to the wheels to be steered. An electric motor,by which an auxiliary force may be exerted directly or indirectly on theoutput member, is positioned on the auxiliary force steering system. Theinput shaft and the output member are connected to each other via atorsionally flexible member so that between the input shaft and theoutput member a limited twisting motion is possible. In steering systemshaving a rack-and-pinion gear, the output member is designed as adriving pinion, and is mechanically connected via a gear rack to thesteerable wheels of a motor vehicle. The gear rack is mechanicallyconnected to a servo motor developed as an electric motor, via areducing gear that may be designed as a worm gear. The output member isconnected to an electric motor via the worm gear. The main components ofthe electric motor are a rotor and a stator. The stator is fixed to thehousing, and the rotor is connected to a worm shaft of the worm gear viaa drive shaft.

[0003] Such an electrical steering system is described, for example, inGerman Published Patent Application No. 197 52 075. This electricalsteering system is made up of an electrical motor-driven worm gearsystem in which the shaft of the worm is held elastically in the gearcase. Play is provided between the worm wheel and the worm of the wormgear. The worm is supported shiftably in the axial direction, and issupported on the gear case via elastic elements. Because of this, thenegative influences transmitted by the electric motor's actuating driveto the steering system may be reduced.

[0004] The electrical steering system described in German PublishedPatent Application No. 197 52 075 has the disadvantage that noisereduction may be achieved, but not noise suppression. Furthermore,noises appearing at the limit stop during travel are not eliminated.Constant functioning cannot be guaranteed over the entire service life,since the elastic elements will have their characteristics changed byouter influences such as temperature and dirt.

[0005] It is an object of the present invention to provide an electricalsteering system which may ensure a constant functioning over its entireservice life in view of the decoupling of structure-borne noise anddamping of the limit stop.

SUMMARY

[0006] The foregoing object may be attained by providing an electricalsteering system as described herein.

[0007] The foregoing object may be achieved by providing an axial andradial decoupling and torsion damping, e.g., by decoupling ofstructure-borne noise of the worm gear system from the steering spindleand the drive pinion. For this purpose, the worm wheel is arranged as acoupling part of an elastic compensation coupling, the other couplingpart of which is formed as a flange which is connected, rotatably fixed,to the input shaft. The two coupling parts are coupled to each other byan elastic spacer, a specified limit stop being provided, which isachieved at a certain torque.

[0008] This may make it possible to achieve an axial and radialdecoupling of the ring gear of the worm wheel from the steering spindle.The rigidity of the ring gear with respect to the input shaft is able tobe changed by adjusting the contour and form of the elastic spacer.

[0009] Further aspects and features of the present invention aredescribed below. However, the present invention is not limited to thefeature combinations set forth below, but rather, further combinationpossibilities of features become apparent to one skilled in the art.

[0010] The present invention is described in greater detail below withreference to an exemplary embodiment represented in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 illustrates the construction of an electrical steeringsystem for motor vehicles, in a schematic representation.

[0012]FIG. 2 is a longitudinal cross-sectional view through theelectrical motor illustrated in FIG. 1.

[0013]FIG. 3 is an exploded representation of the worm wheel illustratedin FIG. 2.

DETAILED DESCRIPTION

[0014] In the exemplary embodiment in FIG. 1, the electrical steeringsystem for motor vehicles includes a steering gear of a rack-and-pinionsteering 1. Such a rack-and-pinion steering 1 is generally conventional,and is therefore not explained in more detail here. An input shaft 2,which is mechanically connected to a steering handwheel 4, for example,via a steering column 3 provided with universal joints, bears a drivepinion of the rack-and-pinion steering.

[0015] A gear rack of rack-and-pinion steering 1, together with two dragrods 5 and 6, form an output member which is connected mechanically towheels to be steered. In addition, the gear rack forms the drive part ofthe steering system.

[0016] By the use of such a steering system, a steering torque may betransmitted from steering handwheel 4 to the wheels to be steered.

[0017] A supporting torque may be exerted on input shaft 2 by anelectric motor 7. In the exemplary embodiment illustrated in FIG. 1,electric motor 7 is positioned so that its axis is located perpendicularto the axis of input shaft 2, and thus of the drive pinion. But its axismay also be positioned at a different angle to the axis of input shaft2. At the same or similar effect, electric motor 7 may be situated sothat its axis is parallel to the axis of input shaft 2, and thus also tothat of the drive pinion or another part of steering column 3. In bothmanners of positioning electric motor 7 described so far, it acts uponinput shaft 2 using the drive pinion of rack-and-pinion steering 1.Electric motor 7 may be positioned so that its axis is parallel orcoaxial to the longitudinal direction of the gear rack ofrack-and-pinion steering 1.

[0018] Electric motor 7 may be configured as an asynchronous motor. Theasynchronous motor may be made up of a rotatable rotor 8 and a fixedwinding 9. The torque is produced by a rotating field specified from theoutside via control and switching elements. Rotor 8 may be configured asa squirrel-cage rotor or as a squirrel-cage induction rotor. Since suchan electric motor does not require permanent magnets, no magnetic fieldis generated during rotation of rotor 8, when there is interference inthe electrical or electronic part of the steering system, which wouldinfluence or hinder the rotary motion of rotor 8. This may ensure thatthe power flow from steering handwheel 4 to the steered wheels is notimpaired in case of interference.

[0019] In the exemplary embodiment illustrated in FIG. 2, winding 9 ofelectric motor 7 is integrated directly into a housing 10 in aspace-saving manner, and is protected from axial and radial motion by astop 11 and an axially prestressed cover 12.

[0020] The torque produced by electric motor 7 is transmitted to inputshaft 2 via a worm gear system made up of worm 13 and worm wheel 14.

[0021]FIG. 3 is an exploded view of the elastic compensation coupling,of which worm wheel 14 illustrated in FIG. 2 is a part.

[0022] It has a ring gear 23, in which worm 13 (FIG. 2) engages. Theother coupling part of the elastic compensation coupling, e.g., flange16, is connected in a rotatably fixed manner to input shaft 2 (see FIGS.1 and 2), e.g., by a connecting piece, the end face of which is marked16 a, and the lateral surface of which is marked 24 d.

[0023] The two parts 14 and 16 of the compensation coupling aresupplemented by a ring-shaped, elastic spacer 17 having processes 20. Inthe assembled state, inner surface 24 b of spacer 17 is arranged onlateral surface 24 d of the connecting piece of flange 16. In thiscontext, in each case two processes 20 encompass one of lugs 25 onflange 16.

[0024] Worm wheel 14 may be arranged with mirror symmetry, and thus mayhave the same aspect on the non-visible reverse side as on the front.After assembly, worm wheel 14 is supported on spacer 17, which in turnis supported on the connecting piece of flange 16. Inner surface 24 c ofworm wheel 14 thus rests on ring outer surface 24 a of spacer 17. Throatdepths 26 of recesses 22 in worm wheel 14 are provided for processes 20of spacer 17. Processes 20 find accommodation in these throat depths 26.

[0025] Although, under certain circumstances, parts 14, 16, and 17 maybe sufficient for fulfilling the functions of an elastic compensationcoupling, the front side of worm wheel 14 is complemented by a secondspacer 27 and a second flange 28 to become an additional compensationcoupling. In the assembled state, flanges 16 and 28 are connected toeach other by studs 21. In addition, an inner toothing of second flange28 engages with a toothing of the connecting piece on flange 16. In theassembled state, second elastic spacer 27 also rests on the connectingpiece of flange 16. These lugs of second flange 28 project in each caseinto the interstice between two closely adjacent processes 20 of spacer27.

[0026] Then, for example, front contact surface 18 a is arranged upagainst the rear side of second flange 28. Rear side contact surface 18b of second spacer 27 is arranged up against contact surface 18 e of athroat depth 26 in worm wheel 14. Lateral contact surfaces 19 a, 19 b ofspacer 17 and 27 rest against lateral contact surfaces 19 c, 19 d oflugs 25 and lateral contact surfaces 19 e, 19 f of throat depths 26 inworm wheel 14.

[0027] Processes 20 thus prevent lugs 25 from directly touching thelateral surfaces of throat depths 26 during the transmission of a torquein one or the other direction. Spacers 17, 27 are also arranged so widethat they prevent direct contact of parts 14 and 26 or 14 and 28 in theaxial direction. And, since the ring-shaped parts of spacers 17, 27 arearranged between lateral surface 24 d of flange 16 and inner surface 24c of worm wheel 14, it is also provided in the radial direction thatdirect contact between the connecting piece of flange 16 and worm wheel14 may be avoided. Spacers 17, 27 thus form buffers between flange 16(and thereby input shaft 2) and worm wheel 14 both in the axial and theradial direction, and also in the tangential direction.

[0028] However, the elastic buffering is not unlimited in the tangentialdirection, because recesses 22 in worm wheel 14, through which studs 21of flange 16 engage, are only a little larger (measured in thetangential direction) than studs 21. This has the result that studs 21and recesses 22 form mutual stops, which take effect when, during thetransmission of an excessively large torque, processes 20 of spacers 17,27 are squeezed together by a certain amount.

[0029] List of reference numerals

[0030]1 rack-and-pinion steering

[0031]2 input shaft

[0032]3 steering column

[0033]4 steering handwheel

[0034]5 drag rod

[0035]6 drag rod

[0036]7 electric motor

[0037]8 rotor

[0038]9 winding

[0039]10 housing

[0040]11 limit stop

[0041]12 cover

[0042]13 worm

[0043]14 worm wheel

[0044]16 flange

[0045]17 spacer

[0046]18 a, b, c, d contact surfaces

[0047]19 a, b, c, d contact surfaces

[0048]20 process

[0049]21 stud

[0050]22 recess

[0051]23 ring gear

[0052]24 a, b, c, d contact surfaces

[0053]25 lug

[0054]26 throat depth

[0055]27 second spacer

[0056]28 second flange

What is claimed is:
 1. An electrical steering system for a motor vehiclehaving an electric motor (7) having a worm gear system which is made upof a worm (13) and a worm wheel (14) coupled to an input shaft (2)having a ring gear (23), characterized by the following features: theworm wheel (14) forms one of the two coupling parts (14, 16) to becoupled of an elastic compensating coupling whose other coupling part(16) is connected rotatably fixed to the input shaft (2), and the twocoupling parts (14, 16) are coupled to each other only by one or aplurality of spacers (17).
 2. The steering system as recited in claim 1,characterized by the following features: a flange (16) is allocated,rotatably fixed, to the input shaft (2), the flange (16) and the wormwheel (14) form the coupling parts, to be coupled to each other, of theelastic compensating coupling for the transmission of torque, the twocoupling parts (16, 14) are separated from each other in the axial,radial and tangential directions by the elastic spacer (17), the spacer(17) has contact surfaces (18 a, 19 a, 19 b, 24 a, 24 b) on which axial,radial and tangential pressure forces act during operation, which areexerted by the corresponding contact surfaces (18 c, 18 d, 19 c, 19 d,24 b, 24 d) of one of the two coupling parts (16, 14), one of the twocoupling parts (16) has at least one stud (21), which engages with playin a larger recess (22) of the other coupling part (14), beginning at acertain torque and the corresponding elastic deformation of the spacer(17), the stud (21) and the recess (22), complement each other afterovercoming the play to form mutual limit stops.
 3. The electricalsteering system as recited in claim 1 or 2, wherein the worm wheel (14)is supported on a connecting piece (16 a) which is a part of the othercoupling part (16), while the elastic spacer (17) is held between them.